1. Field of the Invention
The present invention relates to a liquid crystal display (LCD) device in which a viewing angle is controlled and a method of controlling the viewing angle thereof.
2. Discussion of the Related Art
LCD devices may be driven by a low voltage and may be used in a display of a word processor, a personal computer, or other display applications.
The LCD device has a substrate surface treated to provide a uniform alignment of the liquid crystal and uniformly displays an image.
Due to these, a displayed image on the LCD device varies according to a viewing direction. In other words, the LCD has a viewing angle dependence.
For example, TN and STN LCD devices have a narrow viewing angle, because of light transmission and interruption by a liquid crystal shutter is carried out by controlling a polarization of light using an alignment direction of a rod-shaped liquid crystal molecule.
A viewing angle controlling technique is proposed to improve the viewing angle characteristics of the LCD device. As an example, Japanese Unexamined Patent Application Publication No. Hei 9-19740 discloses a LCD device having two LCDs attached to each other, and a viewing angle controlling structure that collimates light.
A process of controlling the viewing angle of an LCD disclosed in the related art will be described.
FIGS. 1B and 1D are sectional views schematically illustrating a LCD device in which two LCDs are attached to each other and collimated light enters.
First, the collimated light enters a first LCD panel 1. The first LCD panel 1 is identical to a LCD panel of the related art and displays an image.
The light emitted from the first LCD panel 1 enters a second LCD panel 2, and the transmission and scattering of the light is controlled by the second LCD panel 2. The image is displayed at a narrow viewing angle in the transmission mode and at a wide viewing angle in the scattering mode.
In this example, a TN LCD panel is used as the first LCD panel 1 and a polymer dispersed LCD panel is used as the second LCD panel 2.
Meanwhile, when employing the polymer dispersed LCD panel as the second LCD panel 2, as illustrated in FIG. 1D, and because liquid crystal molecules in a liquid crystal droplet that are dispersed within a polymer have a random direction when a voltage is not applied thereto, the incident light is scattered to wide angles (6b,6c) with a brightness similar to that found directly in front of the display 6a. 
A relationship between the brightness and the viewing angle may be represented by a graph as illustrated in FIG. 1C.
Meanwhile, as illustrated in FIG. 1B, because the liquid crystal molecules of the liquid crystal droplet within the polymer are aligned along an electric field when the voltage is applied thereto, the light exits the first LCD panel 1, and the second LCD panel 2 becomes transparent.
Because the collimated light is essentially perpendicular to the LCD panels, a relationship between brightness and a viewing angle when a voltage is applied to the second LCD panel 2. In this mode, the image is represented by a graph as illustrated in FIG. 1A displayed has a narrow viewing angle. As such, in the related art, the control of the viewing angle is carried out by controlling the brightness with respect to a viewing angle by applying a voltage to the second LCD panel 2.
In the related art, because a component to collimate a light from a fluorescent lamp is required and it is necessary to combine polymer dispersed LCD panels to each other, manufacturing costs are high.
Next, other related art is disclosed in Japanese Unexamined Patent Application Publication No. 2004-325563 and will be described.
According to this related art, in a VA mode, the viewing angle is controlled by changing an electrode structure. Electrodes are divided, a gap of an opening between electrodes is slanted, and the shape of electric field is changed to control brightness so as to change the viewing angle.
According to the related art, because the shape of the electrode is determined when manufacturing the electrode and is not changed after manufacturing the LCD panel, a pixel is formed by combining several electrodes' shapes, and a pixel having an optimal viewing angle characteristic is selected and others are not displayed. Thus, optical efficiency is deteriorated.
Moreover, the effect of the viewing angle control, as disclosed in the above patent publication, exhibits maximal brightness in a specific direction, but the effect is not exhibited in other directions.